src/consaver/cons.saver.c

   1 /* This program should be setuid vcsa and /dev/vcsa* should be
   2    owned by the same user too.
   3    Partly rewritten by Jakub Jelinek <jakub@redhat.com>.  */
   4
   5 /* General purpose Linux console screen save/restore server
   6    Copyright (C) 1994, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
   7    2006, 2007 Free Software Foundation, Inc.
   8    Original idea from Unix Interactive Tools version 3.2b (tty.c)
   9    This code requires root privileges.
  10    You may want to make the cons.saver setuid root.
  11    The code should be safe even if it is setuid but who knows?
  12
  13    This program is free software; you can redistribute it and/or modify
  14    it under the terms of the GNU General Public License as published by
  15    the Free Software Foundation; either version 2 of the License, or
  16    (at your option) any later version.
  17
  18    This program is distributed in the hope that it will be useful,
  19    but WITHOUT ANY WARRANTY; without even the implied warranty of
  20    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  21    GNU General Public License for more details.
  22
  23    You should have received a copy of the GNU General Public License
  24    along with this program; if not, write to the Free Software
  25    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  26
  27 /* This code does _not_ need to be setuid root. However, it needs
  28    read/write access to /dev/vcsa* (which is priviledged
  29    operation). You should create user vcsa, make cons.saver setuid
  30    user vcsa, and make all vcsa's owned by user vcsa.
  31
  32    Seeing other peoples consoles is bad thing, but believe me, full
  33    root is even worse. */
  34
  35 /** \file cons.saver.c
  36  *  \brief Source: general purpose Linux console screen save/restore server
  37  *
  38  *  This code does _not_ need to be setuid root. However, it needs
  39  *  read/write access to /dev/vcsa* (which is priviledged
  40  *  operation). You should create user vcsa, make cons.saver setuid
  41  *  user vcsa, and make all vcsa's owned by user vcsa.
  42  *  Seeing other peoples consoles is bad thing, but believe me, full
  43  *  root is even worse.
  44  */
  45
  46 #include <config.h>
  47
  48 #ifndef _GNU_SOURCE
  49 #define _GNU_SOURCE
  50 #endif
  51
  52 #include <stdlib.h>
  53 #include <stdio.h>
  54 #include <string.h>
  55
  56 #include <sys/types.h>
  57 #include <sys/stat.h>
  58 #include <sys/ioctl.h>
  59 #include <fcntl.h>
  60 #include <termios.h>
  61 #include <unistd.h>
  62
  63 #define LINUX_CONS_SAVER_C
  64 #include "cons.saver.h"
  65
  66 static void
  67 send_contents (char *buffer, unsigned int columns, unsigned int rows)
  68 {
  69     unsigned char begin_line = 0, end_line = 0;
  70     unsigned int lastline, lc_index, x;
  71     unsigned char message, outbuf[1024], *p;
  72     unsigned short bytes;
  73
  74     lc_index = 2 * rows * columns;
  75     for (lastline = rows; lastline > 0; lastline--)
  76         for (x = 0; x < columns; x++)
  77         {
  78             lc_index -= 2;
  79             if (buffer[lc_index] != ' ')
  80                 goto out;
  81         }
  82   out:
  83
  84     message = CONSOLE_CONTENTS;
  85     if (write (1, &message, 1) != 1)
  86         return;
  87     if (read (0, &begin_line, 1) != 1)
  88         return;
  89     if (read (0, &end_line, 1) != 1)
  90         return;
  91     if (begin_line > lastline)
  92         begin_line = lastline;
  93     if (end_line > lastline)
  94         end_line = lastline;
  95
  96     lc_index = (end_line - begin_line) * columns;
  97
  98     if (write (1, &bytes, 2) != 2)
  99         return;
 100     if (!bytes)
 101         return;
 102
 103     p = outbuf;
 104     for (lc_index = 2 * begin_line * columns; lc_index < 2 * end_line * columns; lc_index += 2)
 105     {
 106         *p++ = buffer[lc_index];
 107         if (p == outbuf + sizeof (outbuf))
 108         {
 109             if (write (1, outbuf, sizeof (outbuf)) != sizeof (outbuf))
 110                 return;
 111             p = outbuf;
 112         }
 113     }
 114
 115     if (p != outbuf)
 116         if (write (1, outbuf, p - outbuf) < (p - outbuf))
 117             return;
 118 }
 119
 120 static void __attribute__ ((noreturn)) die (void)
 121 {
 122     unsigned char zero = 0;
 123     ssize_t ret;
 124     ret = write (1, &zero, 1);
 125     exit (3);
 126 }
 127
 128 int
 129 main (int argc, char **argv)
 130 {
 131     unsigned char action = 0, console_flag = 3;
 132     int console_fd, vcsa_fd, console_minor, buffer_size;
 133     struct stat st;
 134     uid_t uid, euid;
 135     char *buffer, *tty_name, console_name[16], vcsa_name[16];
 136     const char *p, *q;
 137     struct winsize winsz;
 138
 139     close (2);
 140
 141     if (argc != 2)
 142         die ();
 143
 144     tty_name = argv[1];
 145     if (strnlen (tty_name, 15) == 15 || strncmp (tty_name, "/dev/", 5))
 146         die ();
 147
 148     setsid ();
 149     uid = getuid ();
 150     euid = geteuid ();
 151
 152     if (seteuid (uid) < 0)
 153         die ();
 154     console_fd = open (tty_name, O_RDONLY);
 155     if (console_fd < 0)
 156         die ();
 157     if (fstat (console_fd, &st) < 0 || !S_ISCHR (st.st_mode))
 158         die ();
 159     if ((st.st_rdev & 0xff00) != 0x0400)
 160         die ();
 161     console_minor = (int) (st.st_rdev & 0x00ff);
 162     if (console_minor < 1 || console_minor > 63)
 163         die ();
 164     if (st.st_uid != uid)
 165         die ();
 166
 167     switch (tty_name[5])
 168     {
 169         /* devfs */
 170     case 'v':
 171         p = "/dev/vc/%d";
 172         q = "/dev/vcc/a%d";
 173         break;
 174         /* /dev/ttyN */
 175     case 't':
 176         p = "/dev/tty%d";
 177         q = "/dev/vcsa%d";
 178         break;
 179     default:
 180         die ();
 181         break;
 182     }
 183
 184     snprintf (console_name, sizeof (console_name), p, console_minor);
 185     if (strncmp (console_name, tty_name, sizeof (console_name)) != 0)
 186         die ();
 187
 188     if (seteuid (euid) < 0)
 189         die ();
 190
 191     snprintf (vcsa_name, sizeof (vcsa_name), q, console_minor);
 192     vcsa_fd = open (vcsa_name, O_RDWR);
 193     if (vcsa_fd < 0)
 194         die ();
 195     if (fstat (vcsa_fd, &st) < 0 || !S_ISCHR (st.st_mode))
 196         die ();
 197
 198     if (seteuid (uid) < 0)
 199         die ();
 200
 201     winsz.ws_col = winsz.ws_row = 0;
 202     if (ioctl (console_fd, TIOCGWINSZ, &winsz) < 0
 203         || winsz.ws_col <= 0 || winsz.ws_row <= 0 || winsz.ws_col >= 256 || winsz.ws_row >= 256)
 204         die ();
 205
 206     buffer_size = 4 + 2 * winsz.ws_col * winsz.ws_row;
 207     buffer = calloc (buffer_size, 1);
 208     if (buffer == NULL)
 209         die ();
 210
 211     if (write (1, &console_flag, 1) != 1)
 212         die ();
 213
 214     while (console_flag && read (0, &action, 1) == 1)
 215     {
 216         switch (action)
 217         {
 218         case CONSOLE_DONE:
 219             console_flag = 0;
 220             continue;
 221         case CONSOLE_SAVE:
 222             if (seteuid (euid) < 0
 223                 || lseek (vcsa_fd, 0, 0) != 0
 224                 || fstat (console_fd, &st) < 0 || st.st_uid != uid
 225                 || read (vcsa_fd, buffer, buffer_size) != buffer_size
 226                 || fstat (console_fd, &st) < 0 || st.st_uid != uid)
 227                 memset (buffer, 0, buffer_size);
 228             if (seteuid (uid) < 0)
 229                 die ();
 230             break;
 231         case CONSOLE_RESTORE:
 232             if (seteuid (euid) >= 0
 233                 && lseek (vcsa_fd, 0, 0) == 0 && fstat (console_fd, &st) >= 0 && st.st_uid == uid)
 234                 if (write (vcsa_fd, buffer, buffer_size) != buffer_size)
 235                     die ();
 236             if (seteuid (uid) < 0)
 237                 die ();
 238             break;
 239         case CONSOLE_CONTENTS:
 240             send_contents (buffer + 4, winsz.ws_col, winsz.ws_row);
 241             break;
 242         }
 243
 244         if (write (1, &console_flag, 1) != 1)
 245             die ();
 246     }
 247
 248     exit (0);
 249 }